In the early 1980's, zebra mussels invaded inland waters of the United States, ultimately to include the Mississippi River, Ohio River, adjoining river basins, and most areas of the Great Lakes. They were believed to have been imported from Europe in the ballast water of trans-Atlantic tankers. These shellfish, due to their rapid reproduction and growth, adaptability to most U.S. and Canadian waters, and ability to attach and layer on water system intakes and distribution systems, quickly became a major pest to numerous industries which depended on fresh water intake for cooling water, firewater, and other uses.
Heretofore, Betz Laboratories of Trevose, Pa., developed a process for selective elimination of zebra mussel and like multi-invertibrate in the intakes of industrial water systems and power plants. That process utilized a toxicant for killing of the zebra mussels in the form of an amine compound dispersed into the intake water which inhibits the uptake of oxygen by mussels by attaching to their gills, thus suffocating them, and bentonite swelling clay for detoxification of the compound before discharge of the water back into the receiving body of water. One of these amine compounds was alkyldimethylbenzylammonium chloride, commonly referred to as ADBAC.
In the early years of administration of this process, sodium bentonite clay in three forms was used for detoxification, which included powdered raw clay; a pre-made concentrated clay/water slurry; and a processed, granulated version of bentonite. While the powdered, raw clay was by far the least expensive option from a cost standpoint, the extreme dusting characteristics of this talcum powder-like material made it environmentally and aesthetically unacceptable in the environments of the industrial areas where clamicide applications were being administered. The term “raw clay” as used herein refers to sodium bentonite clay in powdered form. Preferably, the particle size of the clay is on the order of 200 mesh. The pre-made slurry was, of course, dust free, but the cost of this product is quite high in comparison to the other two options, about 15 times raw clay, 3 times granulated clay, and it is somewhat difficult to feed, and also to maintain in a homogeneous dispersion. The processed granulated clay was relatively dust free, could be fed by conventional methods, typically screw feeders which dropped the clay directly into the discharge water, or into funnels which delivered the dry product into eductor throats for slurrification. Thus, granulated clay became the product of choice for larger applications.
Through the mid-1990's, Betz had virtually no competition in this niche market, having patent protection on the only accepted non-oxidizing clamicide process available on the market. The only practical alternative to Clam-Trol, the trade name for the ADBAC product, was continuous chlorination for up to thirty days. Mussels sense chlorine in water, and “clam up” for extended periods of time when chlorine is present. The discharge permits of many facilities did not permit such chlorination practices, so the Betz process was the only alternative, and cost was not an issue. However, in the latter half of the decade, other competitive products/programs came into the market, forcing Betz to reduce treatment costs dramatically, thus cutting profit margins to generally unacceptable levels.
A cost comparison of powdered raw clay versus granulated processed clay revealed that the delivered cost of granulated clay is typically about three times the cost of raw clay. The total “cost of goods” for doing a typical Clam-Trol application could be substantially reduced if raw clay could be used in place of the granulated clay as a detoxifying agent. However, the dusting problem with raw clay remained the one major hurdle that previously prevented its widespread use as a detoxifying agent. If dusting could be minimized or eliminated, using a practical, manageable, and cost-effective process, the only roadblock would be removed, and the inexpensive raw clay, chemically and functionally the same as the granulated clay, could replace the more expensive granulated clay.
Water-driven vacuum eductors have been used for years as one of the options for delivering clay into the discharge water for ADBAC detoxification, but granulated clay was augered into open funnels, using variable speed screw or auger feeders to meter the clay before educting the clay into the water to be treated. The typical process would utilize a large, open receiving hopper for the clay, mounted on top of the screw feeder as part of the screw feeder assembly. Clay was transferred through open atmosphere twice, once to dump bags of granulated clay into the hopper, and a second time to transfer clay from the screw outlet into the eductor funnel. This process was somewhat dusty even with granulated clay. Dusting was overwhelming and totally unacceptable if raw powdered clay was used, wherein windage and clay movement/agitation created breathing problems and other safety hazards, as well as unacceptable housekeeping issues.
Powdered raw bentonite clay provides a low-cost alternative to processed granulated clay or concentrated pre-slurried clay for the detoxification of ADBAC clamicide and similar amine-based clamicides. However, the extreme dusting characteristics of raw clay made it impractical to feed in virtually all industrial and power plant settings where zebra mussel treatments were being administered.